/*
 * Copyright 2013 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.handler.codec.spdy;

import static io.netty.util.internal.ObjectUtil.checkNonEmpty;
import static io.netty.util.internal.ObjectUtil.checkNotNull;

import io.netty.buffer.ByteBuf;

final class SpdyCodecUtil {

    static final int SPDY_SESSION_STREAM_ID = 0;

    static final int SPDY_HEADER_TYPE_OFFSET   = 2;
    static final int SPDY_HEADER_FLAGS_OFFSET  = 4;
    static final int SPDY_HEADER_LENGTH_OFFSET = 5;
    static final int SPDY_HEADER_SIZE          = 8;

    static final int SPDY_MAX_LENGTH = 0xFFFFFF; // Length is a 24-bit field

    static final byte SPDY_DATA_FLAG_FIN = 0x01;

    static final int SPDY_DATA_FRAME          = 0;
    static final int SPDY_SYN_STREAM_FRAME    = 1;
    static final int SPDY_SYN_REPLY_FRAME     = 2;
    static final int SPDY_RST_STREAM_FRAME    = 3;
    static final int SPDY_SETTINGS_FRAME      = 4;
    static final int SPDY_PUSH_PROMISE_FRAME  = 5;
    static final int SPDY_PING_FRAME          = 6;
    static final int SPDY_GOAWAY_FRAME        = 7;
    static final int SPDY_HEADERS_FRAME       = 8;
    static final int SPDY_WINDOW_UPDATE_FRAME = 9;

    static final byte SPDY_FLAG_FIN            = 0x01;
    static final byte SPDY_FLAG_UNIDIRECTIONAL = 0x02;

    static final byte SPDY_SETTINGS_CLEAR         = 0x01;
    static final byte SPDY_SETTINGS_PERSIST_VALUE = 0x01;
    static final byte SPDY_SETTINGS_PERSISTED     = 0x02;

    static final int SPDY_SETTINGS_MAX_ID = 0xFFFFFF; // ID is a 24-bit field

    static final int SPDY_MAX_NV_LENGTH = 0xFFFF; // Length is a 16-bit field

    // Zlib Dictionary
    static final byte[] SPDY_DICT = {
        0x00, 0x00, 0x00, 0x07, 0x6f, 0x70, 0x74, 0x69,   // - - - - o p t i
        0x6f, 0x6e, 0x73, 0x00, 0x00, 0x00, 0x04, 0x68,   // o n s - - - - h
        0x65, 0x61, 0x64, 0x00, 0x00, 0x00, 0x04, 0x70,   // e a d - - - - p
        0x6f, 0x73, 0x74, 0x00, 0x00, 0x00, 0x03, 0x70,   // o s t - - - - p
        0x75, 0x74, 0x00, 0x00, 0x00, 0x06, 0x64, 0x65,   // u t - - - - d e
        0x6c, 0x65, 0x74, 0x65, 0x00, 0x00, 0x00, 0x05,   // l e t e - - - -
        0x74, 0x72, 0x61, 0x63, 0x65, 0x00, 0x00, 0x00,   // t r a c e - - -
        0x06, 0x61, 0x63, 0x63, 0x65, 0x70, 0x74, 0x00,   // - a c c e p t -
        0x00, 0x00, 0x0e, 0x61, 0x63, 0x63, 0x65, 0x70,   // - - - a c c e p
        0x74, 0x2d, 0x63, 0x68, 0x61, 0x72, 0x73, 0x65,   // t - c h a r s e
        0x74, 0x00, 0x00, 0x00, 0x0f, 0x61, 0x63, 0x63,   // t - - - - a c c
        0x65, 0x70, 0x74, 0x2d, 0x65, 0x6e, 0x63, 0x6f,   // e p t - e n c o
        0x64, 0x69, 0x6e, 0x67, 0x00, 0x00, 0x00, 0x0f,   // d i n g - - - -
        0x61, 0x63, 0x63, 0x65, 0x70, 0x74, 0x2d, 0x6c,   // a c c e p t - l
        0x61, 0x6e, 0x67, 0x75, 0x61, 0x67, 0x65, 0x00,   // a n g u a g e -
        0x00, 0x00, 0x0d, 0x61, 0x63, 0x63, 0x65, 0x70,   // - - - a c c e p
        0x74, 0x2d, 0x72, 0x61, 0x6e, 0x67, 0x65, 0x73,   // t - r a n g e s
        0x00, 0x00, 0x00, 0x03, 0x61, 0x67, 0x65, 0x00,   // - - - - a g e -
        0x00, 0x00, 0x05, 0x61, 0x6c, 0x6c, 0x6f, 0x77,   // - - - a l l o w
        0x00, 0x00, 0x00, 0x0d, 0x61, 0x75, 0x74, 0x68,   // - - - - a u t h
        0x6f, 0x72, 0x69, 0x7a, 0x61, 0x74, 0x69, 0x6f,   // o r i z a t i o
        0x6e, 0x00, 0x00, 0x00, 0x0d, 0x63, 0x61, 0x63,   // n - - - - c a c
        0x68, 0x65, 0x2d, 0x63, 0x6f, 0x6e, 0x74, 0x72,   // h e - c o n t r
        0x6f, 0x6c, 0x00, 0x00, 0x00, 0x0a, 0x63, 0x6f,   // o l - - - - c o
        0x6e, 0x6e, 0x65, 0x63, 0x74, 0x69, 0x6f, 0x6e,   // n n e c t i o n
        0x00, 0x00, 0x00, 0x0c, 0x63, 0x6f, 0x6e, 0x74,   // - - - - c o n t
        0x65, 0x6e, 0x74, 0x2d, 0x62, 0x61, 0x73, 0x65,   // e n t - b a s e
        0x00, 0x00, 0x00, 0x10, 0x63, 0x6f, 0x6e, 0x74,   // - - - - c o n t
        0x65, 0x6e, 0x74, 0x2d, 0x65, 0x6e, 0x63, 0x6f,   // e n t - e n c o
        0x64, 0x69, 0x6e, 0x67, 0x00, 0x00, 0x00, 0x10,   // d i n g - - - -
        0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, 0x74, 0x2d,   // c o n t e n t -
        0x6c, 0x61, 0x6e, 0x67, 0x75, 0x61, 0x67, 0x65,   // l a n g u a g e
        0x00, 0x00, 0x00, 0x0e, 0x63, 0x6f, 0x6e, 0x74,   // - - - - c o n t
        0x65, 0x6e, 0x74, 0x2d, 0x6c, 0x65, 0x6e, 0x67,   // e n t - l e n g
        0x74, 0x68, 0x00, 0x00, 0x00, 0x10, 0x63, 0x6f,   // t h - - - - c o
        0x6e, 0x74, 0x65, 0x6e, 0x74, 0x2d, 0x6c, 0x6f,   // n t e n t - l o
        0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00,   // c a t i o n - -
        0x00, 0x0b, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e,   // - - c o n t e n
        0x74, 0x2d, 0x6d, 0x64, 0x35, 0x00, 0x00, 0x00,   // t - m d 5 - - -
        0x0d, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, 0x74,   // - c o n t e n t
        0x2d, 0x72, 0x61, 0x6e, 0x67, 0x65, 0x00, 0x00,   // - r a n g e - -
        0x00, 0x0c, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e,   // - - c o n t e n
        0x74, 0x2d, 0x74, 0x79, 0x70, 0x65, 0x00, 0x00,   // t - t y p e - -
        0x00, 0x04, 0x64, 0x61, 0x74, 0x65, 0x00, 0x00,   // - - d a t e - -
        0x00, 0x04, 0x65, 0x74, 0x61, 0x67, 0x00, 0x00,   // - - e t a g - -
        0x00, 0x06, 0x65, 0x78, 0x70, 0x65, 0x63, 0x74,   // - - e x p e c t
        0x00, 0x00, 0x00, 0x07, 0x65, 0x78, 0x70, 0x69,   // - - - - e x p i
        0x72, 0x65, 0x73, 0x00, 0x00, 0x00, 0x04, 0x66,   // r e s - - - - f
        0x72, 0x6f, 0x6d, 0x00, 0x00, 0x00, 0x04, 0x68,   // r o m - - - - h
        0x6f, 0x73, 0x74, 0x00, 0x00, 0x00, 0x08, 0x69,   // o s t - - - - i
        0x66, 0x2d, 0x6d, 0x61, 0x74, 0x63, 0x68, 0x00,   // f - m a t c h -
        0x00, 0x00, 0x11, 0x69, 0x66, 0x2d, 0x6d, 0x6f,   // - - - i f - m o
        0x64, 0x69, 0x66, 0x69, 0x65, 0x64, 0x2d, 0x73,   // d i f i e d - s
        0x69, 0x6e, 0x63, 0x65, 0x00, 0x00, 0x00, 0x0d,   // i n c e - - - -
        0x69, 0x66, 0x2d, 0x6e, 0x6f, 0x6e, 0x65, 0x2d,   // i f - n o n e -
        0x6d, 0x61, 0x74, 0x63, 0x68, 0x00, 0x00, 0x00,   // m a t c h - - -
        0x08, 0x69, 0x66, 0x2d, 0x72, 0x61, 0x6e, 0x67,   // - i f - r a n g
        0x65, 0x00, 0x00, 0x00, 0x13, 0x69, 0x66, 0x2d,   // e - - - - i f -
        0x75, 0x6e, 0x6d, 0x6f, 0x64, 0x69, 0x66, 0x69,   // u n m o d i f i
        0x65, 0x64, 0x2d, 0x73, 0x69, 0x6e, 0x63, 0x65,   // e d - s i n c e
        0x00, 0x00, 0x00, 0x0d, 0x6c, 0x61, 0x73, 0x74,   // - - - - l a s t
        0x2d, 0x6d, 0x6f, 0x64, 0x69, 0x66, 0x69, 0x65,   // - m o d i f i e
        0x64, 0x00, 0x00, 0x00, 0x08, 0x6c, 0x6f, 0x63,   // d - - - - l o c
        0x61, 0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00, 0x00,   // a t i o n - - -
        0x0c, 0x6d, 0x61, 0x78, 0x2d, 0x66, 0x6f, 0x72,   // - m a x - f o r
        0x77, 0x61, 0x72, 0x64, 0x73, 0x00, 0x00, 0x00,   // w a r d s - - -
        0x06, 0x70, 0x72, 0x61, 0x67, 0x6d, 0x61, 0x00,   // - p r a g m a -
        0x00, 0x00, 0x12, 0x70, 0x72, 0x6f, 0x78, 0x79,   // - - - p r o x y
        0x2d, 0x61, 0x75, 0x74, 0x68, 0x65, 0x6e, 0x74,   // - a u t h e n t
        0x69, 0x63, 0x61, 0x74, 0x65, 0x00, 0x00, 0x00,   // i c a t e - - -
        0x13, 0x70, 0x72, 0x6f, 0x78, 0x79, 0x2d, 0x61,   // - p r o x y - a
        0x75, 0x74, 0x68, 0x6f, 0x72, 0x69, 0x7a, 0x61,   // u t h o r i z a
        0x74, 0x69, 0x6f, 0x6e, 0x00, 0x00, 0x00, 0x05,   // t i o n - - - -
        0x72, 0x61, 0x6e, 0x67, 0x65, 0x00, 0x00, 0x00,   // r a n g e - - -
        0x07, 0x72, 0x65, 0x66, 0x65, 0x72, 0x65, 0x72,   // - r e f e r e r
        0x00, 0x00, 0x00, 0x0b, 0x72, 0x65, 0x74, 0x72,   // - - - - r e t r
        0x79, 0x2d, 0x61, 0x66, 0x74, 0x65, 0x72, 0x00,   // y - a f t e r -
        0x00, 0x00, 0x06, 0x73, 0x65, 0x72, 0x76, 0x65,   // - - - s e r v e
        0x72, 0x00, 0x00, 0x00, 0x02, 0x74, 0x65, 0x00,   // r - - - - t e -
        0x00, 0x00, 0x07, 0x74, 0x72, 0x61, 0x69, 0x6c,   // - - - t r a i l
        0x65, 0x72, 0x00, 0x00, 0x00, 0x11, 0x74, 0x72,   // e r - - - - t r
        0x61, 0x6e, 0x73, 0x66, 0x65, 0x72, 0x2d, 0x65,   // a n s f e r - e
        0x6e, 0x63, 0x6f, 0x64, 0x69, 0x6e, 0x67, 0x00,   // n c o d i n g -
        0x00, 0x00, 0x07, 0x75, 0x70, 0x67, 0x72, 0x61,   // - - - u p g r a
        0x64, 0x65, 0x00, 0x00, 0x00, 0x0a, 0x75, 0x73,   // d e - - - - u s
        0x65, 0x72, 0x2d, 0x61, 0x67, 0x65, 0x6e, 0x74,   // e r - a g e n t
        0x00, 0x00, 0x00, 0x04, 0x76, 0x61, 0x72, 0x79,   // - - - - v a r y
        0x00, 0x00, 0x00, 0x03, 0x76, 0x69, 0x61, 0x00,   // - - - - v i a -
        0x00, 0x00, 0x07, 0x77, 0x61, 0x72, 0x6e, 0x69,   // - - - w a r n i
        0x6e, 0x67, 0x00, 0x00, 0x00, 0x10, 0x77, 0x77,   // n g - - - - w w
        0x77, 0x2d, 0x61, 0x75, 0x74, 0x68, 0x65, 0x6e,   // w - a u t h e n
        0x74, 0x69, 0x63, 0x61, 0x74, 0x65, 0x00, 0x00,   // t i c a t e - -
        0x00, 0x06, 0x6d, 0x65, 0x74, 0x68, 0x6f, 0x64,   // - - m e t h o d
        0x00, 0x00, 0x00, 0x03, 0x67, 0x65, 0x74, 0x00,   // - - - - g e t -
        0x00, 0x00, 0x06, 0x73, 0x74, 0x61, 0x74, 0x75,   // - - - s t a t u
        0x73, 0x00, 0x00, 0x00, 0x06, 0x32, 0x30, 0x30,   // s - - - - 2 0 0
        0x20, 0x4f, 0x4b, 0x00, 0x00, 0x00, 0x07, 0x76,   // - O K - - - - v
        0x65, 0x72, 0x73, 0x69, 0x6f, 0x6e, 0x00, 0x00,   // e r s i o n - -
        0x00, 0x08, 0x48, 0x54, 0x54, 0x50, 0x2f, 0x31,   // - - H T T P - 1
        0x2e, 0x31, 0x00, 0x00, 0x00, 0x03, 0x75, 0x72,   // - 1 - - - - u r
        0x6c, 0x00, 0x00, 0x00, 0x06, 0x70, 0x75, 0x62,   // l - - - - p u b
        0x6c, 0x69, 0x63, 0x00, 0x00, 0x00, 0x0a, 0x73,   // l i c - - - - s
        0x65, 0x74, 0x2d, 0x63, 0x6f, 0x6f, 0x6b, 0x69,   // e t - c o o k i
        0x65, 0x00, 0x00, 0x00, 0x0a, 0x6b, 0x65, 0x65,   // e - - - - k e e
        0x70, 0x2d, 0x61, 0x6c, 0x69, 0x76, 0x65, 0x00,   // p - a l i v e -
        0x00, 0x00, 0x06, 0x6f, 0x72, 0x69, 0x67, 0x69,   // - - - o r i g i
        0x6e, 0x31, 0x30, 0x30, 0x31, 0x30, 0x31, 0x32,   // n 1 0 0 1 0 1 2
        0x30, 0x31, 0x32, 0x30, 0x32, 0x32, 0x30, 0x35,   // 0 1 2 0 2 2 0 5
        0x32, 0x30, 0x36, 0x33, 0x30, 0x30, 0x33, 0x30,   // 2 0 6 3 0 0 3 0
        0x32, 0x33, 0x30, 0x33, 0x33, 0x30, 0x34, 0x33,   // 2 3 0 3 3 0 4 3
        0x30, 0x35, 0x33, 0x30, 0x36, 0x33, 0x30, 0x37,   // 0 5 3 0 6 3 0 7
        0x34, 0x30, 0x32, 0x34, 0x30, 0x35, 0x34, 0x30,   // 4 0 2 4 0 5 4 0
        0x36, 0x34, 0x30, 0x37, 0x34, 0x30, 0x38, 0x34,   // 6 4 0 7 4 0 8 4
        0x30, 0x39, 0x34, 0x31, 0x30, 0x34, 0x31, 0x31,   // 0 9 4 1 0 4 1 1
        0x34, 0x31, 0x32, 0x34, 0x31, 0x33, 0x34, 0x31,   // 4 1 2 4 1 3 4 1
        0x34, 0x34, 0x31, 0x35, 0x34, 0x31, 0x36, 0x34,   // 4 4 1 5 4 1 6 4
        0x31, 0x37, 0x35, 0x30, 0x32, 0x35, 0x30, 0x34,   // 1 7 5 0 2 5 0 4
        0x35, 0x30, 0x35, 0x32, 0x30, 0x33, 0x20, 0x4e,   // 5 0 5 2 0 3 - N
        0x6f, 0x6e, 0x2d, 0x41, 0x75, 0x74, 0x68, 0x6f,   // o n - A u t h o
        0x72, 0x69, 0x74, 0x61, 0x74, 0x69, 0x76, 0x65,   // r i t a t i v e
        0x20, 0x49, 0x6e, 0x66, 0x6f, 0x72, 0x6d, 0x61,   // - I n f o r m a
        0x74, 0x69, 0x6f, 0x6e, 0x32, 0x30, 0x34, 0x20,   // t i o n 2 0 4 -
        0x4e, 0x6f, 0x20, 0x43, 0x6f, 0x6e, 0x74, 0x65,   // N o - C o n t e
        0x6e, 0x74, 0x33, 0x30, 0x31, 0x20, 0x4d, 0x6f,   // n t 3 0 1 - M o
        0x76, 0x65, 0x64, 0x20, 0x50, 0x65, 0x72, 0x6d,   // v e d - P e r m
        0x61, 0x6e, 0x65, 0x6e, 0x74, 0x6c, 0x79, 0x34,   // a n e n t l y 4
        0x30, 0x30, 0x20, 0x42, 0x61, 0x64, 0x20, 0x52,   // 0 0 - B a d - R
        0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x34, 0x30,   // e q u e s t 4 0
        0x31, 0x20, 0x55, 0x6e, 0x61, 0x75, 0x74, 0x68,   // 1 - U n a u t h
        0x6f, 0x72, 0x69, 0x7a, 0x65, 0x64, 0x34, 0x30,   // o r i z e d 4 0
        0x33, 0x20, 0x46, 0x6f, 0x72, 0x62, 0x69, 0x64,   // 3 - F o r b i d
        0x64, 0x65, 0x6e, 0x34, 0x30, 0x34, 0x20, 0x4e,   // d e n 4 0 4 - N
        0x6f, 0x74, 0x20, 0x46, 0x6f, 0x75, 0x6e, 0x64,   // o t - F o u n d
        0x35, 0x30, 0x30, 0x20, 0x49, 0x6e, 0x74, 0x65,   // 5 0 0 - I n t e
        0x72, 0x6e, 0x61, 0x6c, 0x20, 0x53, 0x65, 0x72,   // r n a l - S e r
        0x76, 0x65, 0x72, 0x20, 0x45, 0x72, 0x72, 0x6f,   // v e r - E r r o
        0x72, 0x35, 0x30, 0x31, 0x20, 0x4e, 0x6f, 0x74,   // r 5 0 1 - N o t
        0x20, 0x49, 0x6d, 0x70, 0x6c, 0x65, 0x6d, 0x65,   // - I m p l e m e
        0x6e, 0x74, 0x65, 0x64, 0x35, 0x30, 0x33, 0x20,   // n t e d 5 0 3 -
        0x53, 0x65, 0x72, 0x76, 0x69, 0x63, 0x65, 0x20,   // S e r v i c e -
        0x55, 0x6e, 0x61, 0x76, 0x61, 0x69, 0x6c, 0x61,   // U n a v a i l a
        0x62, 0x6c, 0x65, 0x4a, 0x61, 0x6e, 0x20, 0x46,   // b l e J a n - F
        0x65, 0x62, 0x20, 0x4d, 0x61, 0x72, 0x20, 0x41,   // e b - M a r - A
        0x70, 0x72, 0x20, 0x4d, 0x61, 0x79, 0x20, 0x4a,   // p r - M a y - J
        0x75, 0x6e, 0x20, 0x4a, 0x75, 0x6c, 0x20, 0x41,   // u n - J u l - A
        0x75, 0x67, 0x20, 0x53, 0x65, 0x70, 0x74, 0x20,   // u g - S e p t -
        0x4f, 0x63, 0x74, 0x20, 0x4e, 0x6f, 0x76, 0x20,   // O c t - N o v -
        0x44, 0x65, 0x63, 0x20, 0x30, 0x30, 0x3a, 0x30,   // D e c - 0 0 - 0
        0x30, 0x3a, 0x30, 0x30, 0x20, 0x4d, 0x6f, 0x6e,   // 0 - 0 0 - M o n
        0x2c, 0x20, 0x54, 0x75, 0x65, 0x2c, 0x20, 0x57,   // - - T u e - - W
        0x65, 0x64, 0x2c, 0x20, 0x54, 0x68, 0x75, 0x2c,   // e d - - T h u -
        0x20, 0x46, 0x72, 0x69, 0x2c, 0x20, 0x53, 0x61,   // - F r i - - S a
        0x74, 0x2c, 0x20, 0x53, 0x75, 0x6e, 0x2c, 0x20,   // t - - S u n - -
        0x47, 0x4d, 0x54, 0x63, 0x68, 0x75, 0x6e, 0x6b,   // G M T c h u n k
        0x65, 0x64, 0x2c, 0x74, 0x65, 0x78, 0x74, 0x2f,   // e d - t e x t -
        0x68, 0x74, 0x6d, 0x6c, 0x2c, 0x69, 0x6d, 0x61,   // h t m l - i m a
        0x67, 0x65, 0x2f, 0x70, 0x6e, 0x67, 0x2c, 0x69,   // g e - p n g - i
        0x6d, 0x61, 0x67, 0x65, 0x2f, 0x6a, 0x70, 0x67,   // m a g e - j p g
        0x2c, 0x69, 0x6d, 0x61, 0x67, 0x65, 0x2f, 0x67,   // - i m a g e - g
        0x69, 0x66, 0x2c, 0x61, 0x70, 0x70, 0x6c, 0x69,   // i f - a p p l i
        0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x2f, 0x78,   // c a t i o n - x
        0x6d, 0x6c, 0x2c, 0x61, 0x70, 0x70, 0x6c, 0x69,   // m l - a p p l i
        0x63, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x2f, 0x78,   // c a t i o n - x
        0x68, 0x74, 0x6d, 0x6c, 0x2b, 0x78, 0x6d, 0x6c,   // h t m l - x m l
        0x2c, 0x74, 0x65, 0x78, 0x74, 0x2f, 0x70, 0x6c,   // - t e x t - p l
        0x61, 0x69, 0x6e, 0x2c, 0x74, 0x65, 0x78, 0x74,   // a i n - t e x t
        0x2f, 0x6a, 0x61, 0x76, 0x61, 0x73, 0x63, 0x72,   // - j a v a s c r
        0x69, 0x70, 0x74, 0x2c, 0x70, 0x75, 0x62, 0x6c,   // i p t - p u b l
        0x69, 0x63, 0x70, 0x72, 0x69, 0x76, 0x61, 0x74,   // i c p r i v a t
        0x65, 0x6d, 0x61, 0x78, 0x2d, 0x61, 0x67, 0x65,   // e m a x - a g e
        0x3d, 0x67, 0x7a, 0x69, 0x70, 0x2c, 0x64, 0x65,   // - g z i p - d e
        0x66, 0x6c, 0x61, 0x74, 0x65, 0x2c, 0x73, 0x64,   // f l a t e - s d
        0x63, 0x68, 0x63, 0x68, 0x61, 0x72, 0x73, 0x65,   // c h c h a r s e
        0x74, 0x3d, 0x75, 0x74, 0x66, 0x2d, 0x38, 0x63,   // t - u t f - 8 c
        0x68, 0x61, 0x72, 0x73, 0x65, 0x74, 0x3d, 0x69,   // h a r s e t - i
        0x73, 0x6f, 0x2d, 0x38, 0x38, 0x35, 0x39, 0x2d,   // s o - 8 8 5 9 -
        0x31, 0x2c, 0x75, 0x74, 0x66, 0x2d, 0x2c, 0x2a,   // 1 - u t f - - -
        0x2c, 0x65, 0x6e, 0x71, 0x3d, 0x30, 0x2e          // - e n q - 0 -
    };

    private SpdyCodecUtil() {
    }

    /**
     * Reads a big-endian unsigned short integer from the buffer.
     */
    static int getUnsignedShort(ByteBuf buf, int offset) {
        return (buf.getByte(offset)     & 0xFF) << 8 |
                buf.getByte(offset + 1) & 0xFF;
    }

    /**
     * Reads a big-endian unsigned medium integer from the buffer.
     */
    static int getUnsignedMedium(ByteBuf buf, int offset) {
        return (buf.getByte(offset)     & 0xFF) << 16 |
               (buf.getByte(offset + 1) & 0xFF) <<  8 |
                buf.getByte(offset + 2) & 0xFF;
    }

    /**
     * Reads a big-endian (31-bit) integer from the buffer.
     */
    static int getUnsignedInt(ByteBuf buf, int offset) {
        return (buf.getByte(offset)     & 0x7F) << 24 |
               (buf.getByte(offset + 1) & 0xFF) << 16 |
               (buf.getByte(offset + 2) & 0xFF) <<  8 |
                buf.getByte(offset + 3) & 0xFF;
    }

    /**
     * Reads a big-endian signed integer from the buffer.
     */
    static int getSignedInt(ByteBuf buf, int offset) {
        return (buf.getByte(offset)     & 0xFF) << 24 |
               (buf.getByte(offset + 1) & 0xFF) << 16 |
               (buf.getByte(offset + 2) & 0xFF) <<  8 |
                buf.getByte(offset + 3) & 0xFF;
    }

    /**
     * Returns {@code true} if ID is for a server initiated stream or ping.
     */
    static boolean isServerId(int id) {
        // Server initiated streams and pings have even IDs
        return id % 2 == 0;
    }

    /**
     * Validate a SPDY header name.
     */
    static void validateHeaderName(CharSequence name) {
        checkNonEmpty(name, "name");
        // Since name may only contain ascii characters, for valid names
        // name.length() returns the number of bytes when UTF-8 encoded.
        if (name.length() > SPDY_MAX_NV_LENGTH) {
            throw new IllegalArgumentException(
                    "name exceeds allowable length: " + name);
        }
        for (int i = 0; i < name.length(); i ++) {
            char c = name.charAt(i);
            if (c == 0) {
                throw new IllegalArgumentException(
                        "name contains null character: " + name);
            }
            if (c >= 'A' && c <= 'Z') {
                throw new IllegalArgumentException("name must be all lower case.");
            }
            if (c > 127) {
                throw new IllegalArgumentException(
                        "name contains non-ascii character: " + name);
            }
        }
    }

    /**
     * Validate a SPDY header value. Does not validate max length.
     */
    static void validateHeaderValue(CharSequence value) {
        checkNotNull(value, "value");
        for (int i = 0; i < value.length(); i ++) {
            char c = value.charAt(i);
            if (c == 0) {
                throw new IllegalArgumentException(
                        "value contains null character: " + value);
            }
        }
    }
}
